382 Dr. G. Bird on certain Properties acquired by the 



nexion made with the galvanometer; the deviation of the 

 needles produced lie attributes to minute films of acid and 

 alkali adhering to the electrodes, combining to re-form the 

 salt electrolyzed by the previous passage of the battery cur- 

 rent, and thus give rise to a weak secondary current in a di- 

 rection the reverse of that of the battery. This explanation 

 will, I think- hardly apply in the above experiments, as the 

 electrolyte was dilute sulphuric acid, and no other elements 

 present, separable by the electricity, whose reunion could ex- 

 cite a current except oxygen and hydrogen ; and even if the 

 polar state be attributed to the previous decomposition of in- 

 finitely minute quantities of saline maitev accidentally present, 

 still it would require more satisfactory evidence than we yet 

 possess to show that the recombination of the separated ele- 

 ments of the salts would develop sufficient electricity to act 

 with such energy on the galvanometer, particularly as the 

 late experiments of Dr. Mohr, of Coblentz, have rendered it 

 very doubtful whether electric currents are ever set in motion 

 during the combination of an alkali with an acid except in the 

 solitary case of nitric acid, and which then may, perhaps, be 

 attributed to a very different cause*. 



For the purpose of discovering some clue to the cause of 

 this curious phaenomenon, the following experiments were per- 

 formed. 



Exp. 6. The cup A was connected to the negative and B 

 to the positive wire of the battery ; the connexion being re- 

 moved, the deviation produced by connecting A and B to the 

 galvanometer was ascertained to be 90° : the glass basin was 

 then emptied of its acid, and set aside for 48 hours ; at the 

 expiration of that time it was refilled with dilute sulphuric 

 acid and connected again with the galvanometer ; the needles 

 deviated to 6° in the same direction as in Exp. 5. 



Exp. 7. The galvanometer wires being removed, the amal- 

 gamated zinc rod was immersed in the acid contained in the 

 basin, its two wires dipping into the cups A and B ; gas was 

 as before evolved from both platina plates ; this was collected 

 in separate tubes and measured. 



inches. 

 In the tube over the plate A was found 1 '95 gas = 1 •() 



, B 2-20 — r= 1-13 



Exp. 8. The cups A and B were connected with the battery 

 as in Exp. 6, for five minutes ; the apparatus was removed from 

 the battery, and set aside for 48 hours full of the acid. On 



* " Ueber Becquerel's Einfache Kette, deren Strom aiis dem Verbin- 

 diing von Siiure und Alkali enstehen soil." — Von Dr. Mohr, Poggcndorf, 

 Annalen, xlii. p. 76. 



